First they are both crime/investigation shows, I guess TEN is darker than MR.BRAIN atmospherically but i don't think that's makes the point of liking one and not there other. Both feature Crimes/evidence that seem impossible and illogical. Both feature a back story of seemingly unreachable criminal with which the last ep revolves around. ( MR is Jap and TEN is Korean)
Both series have a similar style (plus, the working title for M was so close to TEN that I thought it would be a spinoff at first), both series have a similar atmosphere while TEN is actually about murder cases compared to those cases about missing people.
Also the director Lee Seung-young was involved in the creation of both series, and both are OCN Original series (OCN is a channel with lots of experience when it comes to crime series)
Also the director Lee Seung-young was involved in the creation of both series, and both are OCN Original series (OCN is a channel with lots of experience when it comes to crime series)